The main objective of the proposed research is to determine the role of protein kinase C (Ca++/phospholipid-dependent protein kinase) in astrocyte function. One major focus will be on the mechanism by which protein kinase C regulates astrocyte morphology and the identification of phosphoproteins involved in this process. An important aspect of the response of astrocyte to brain trauma involves a change in morphology. ln addition to hypertrophy and increase branching of processes, in some cases (e.g. stab wound) astrocyte processes orient toward the lesion site and foot processes develop to form a glial membrane around the wound. Clearly, an understanding of the mechanisms which underlie changes in astrocyte morphology will be important for the development of better therapies for the treatment of brain injuries. Additionally, changes in astrocyte morphology are associated with differentiation and may also play a role in regulation neuron- neuron contact to allow for the syncronous firing of neurons. The basic approach to be used will be to search for and identify phosphoprotein substrates for protein kinase C, to correlate the phos-phorylation of these proteins with changes in morphology, and to compare these phosphoproteins and their sites of phosphorylation to the pattern of protein phosphorylated observed in response to the activation of the cyclic AMP dependent protein kinase (a kinase also involved in the regulation of astrocyte morphology). The second major focus will be to evaluate the broader physiological role of protein kinase C in astrocytes. This will include studies concerning the mechanisms involved in the regulation of protein kinase C activity in astrocytes and the identification of extracellular signals which activate this kinase. Also included will be studies concerning the effect of protein kinase C activation on various parameters, besides morphology, associated with gliosis and differentiation. This will include the regulation of intracellular pH and free (Ca++), the expression of GFAP, glutamine synthetase activity, and astrocyte mitogenesis. From the studies outlined in this proposal concerning the role of protein kinase C in astrocytes, new insight will be gained concerning the mechanisms which underlie astrocyte function in brain and which regulate the astrocytic response observed with various types of brain trauma including brain grafts, and in neurodegenerative diseases such as Alzheimer's and Huntington's disease.